This study demonstrates that humidity, temperature, and the interlayer anions influence ionic conductivities of Mg-Al layered double hydroxides (LDHs) intercalated with inorganic anions. Results show that Mg-Al LDH intercalated with Br(-) exhibited the highest ionic conductivity among Mg-Al LDHs intercalated with CO(3)(2-), Cl(-), Br(-), NO(3)(-) and SO(4)(2-). Its ionic conductivity was 1.1 x 10(-2) S cm(-1) at 80 degrees C under 80% relative humidity. The electromotive force for the hydroxide ion concentration cell using Mg-Al CO(3)(2-) LDH showed the same behavior with that using an anion exchange membrane, indicating that Mg-Al CO(3)(2-) LDH can be a hydroxide ion conductor. (C) 2010 Elsevier B.V. All rights reserved.